let screen_width = window.screen.width;
let screen_height = window.screen.height;
if (screen_width < 1600) {
    // alert("小屏幕");
    document.write('<link href="css/index/mainStyle_small.css" rel="stylesheet">');
} else {
    // alert("大屏幕");
    document.write('<link href="css/index/mainStyle.css" rel="stylesheet"></link>');
}